Process of making a solid state energy conversion device

ABSTRACT

A solid state energy conversion device and method of making is disclosed for converting energy between electromagnetic and electrical energy. The solid state energy conversion device comprises a wide bandgap semiconductor material having a first doped region. A thermal energy beam is directed onto the first doped region of the wide bandgap semiconductor material in the presence of a doping gas for converting a portion of the first doped region into a second doped region in the wide bandgap semiconductor material. A first and a second Ohmic contact are applied to the first and the second doped regions of the wide bandgap semiconductor material. In one embodiment, the solid state energy conversion device operates as a light emitting device to produce electromagnetic radiation upon the application of electrical power to the first and second Ohmic contacts.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.11/900,488 filed Sep. 12, 2007 now U.S. Pat. No. 8,067,303. ApplicationSer. No. 11/900,488 filed Sep. 12, 2007 claims benefit of U.S.provisional application No. 60/844,044 filed Sep. 12, 2006 and U.S.Patent provisional application No. 60/859,648 filed Nov. 17, 2006. Allsubject matter of application Ser. No. 11/900,488, application No.60/844,044 and application No. 60/859,648 is incorporated herein byreference as if full set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to solid state devices and more particularly tosolid state devices for converting energy between electromagnetic andelectrical energy such as light emitting device and photovoltaic device.

2. Background of the Invention

A variety of semiconductors including GaN (Gallium Nitride), GaP(Gallium Phosphide), AlGaAs (Aluminum Gallium Arsenide), InP (IndiumPhosphide), Si (Silicon) and SiC are currently being studied for lightemitting diode (LED) applications. Recently, efficient luminescence hasbeen discovered in silicon, which is an indirect bandgap semiconductor,due to alteration of its defect states [Wai Lek Ng, et al, Nature, Vol.410, Issue 8 (2001)]. However in SiC, an indirect bandgap wide-bandgapsemiconductor (WBGS) generally emitting in the blue spectra, noefficient radiative isoelectronic trap has been discovered; consequentlydevelopment of this LED material has languished. Other recent papersshow that SiC LEDs have potential for high quantum efficiency [a) S. I.Vlaskina, “Silicon Carbide LED”, Semiconductor Physics, QuantumElectronics & Optoelectronics, 2002, Vol. 5, No. 1, pp 71-75, b) S.Kamiyama et al, “Extremely high quantum efficiency ofdonor-acceptor-pair emission in N- and B-doped 6H—SiC, JAP, 99, 093108(2006).].

P-type doping, particularly exhibiting low resistivity, has been adrawback for wide-bandgap semiconductor LED material candidates. Ionimplantation and thermal diffusion are currently the most widely usedtechniques for doping semiconductors. The energy scattered by thedecelerating ions leads to crystal damage by introducing point defectsand the formation of amorphous material. Post ion implantation hightemperature annealing isothermally heats the wafer inducing undesirabledopant diffusion in previously prepared under layers.

Doping is one of the challenges for wide bandgap semiconductors,particualry SiC, device fabrication due to its hardness, chemicalinertness and the low diffusion coefficient of most impurities I. A.Salama, Ph.D. Dissertation, University of Central Florida, Spring(2003). Current doping methods used for SiC device fabrication includeepilayer doping and ion implantation. Maximum doping concentration islimited by the solubility dopant depth is limited by the mass diffusioncoefficient of the dopant in the wide bandgap semiconductor substrate.Epilayer doping is in situ doping during chemical vapor depositionepitaxial growth and is limited in SiC to nitrogen (N) or phosphorous(P) for n-type, aluminum (Al) or boron (B) for p-type and vanadium (V)for semi-insulating type. Ion implantation is the most common dopingtechnique used used for wide bandgap semiconductor devices. This processgenerates implantation-induced defect centers including amorphitizationin the wafer and requires high annealing temperatures to remove thesedefects and to electrically activate the dopants. In SiC some defectsremain after annealing at temperatures up to 1700° C. [Z. Tian., N. R.Quick. and A. Kar, Acta Materialia, Vol. 53, (2005), pp. 2835-2844].Annealing at these temperatures can cause severe surface damage due tosilicon sublimation and redistribution [Z. Tian, N. R. Quick and A. Kar,Acta Materialia, 54, 4273, (2006)]. In summary conventional dopingprocesses limit the dopant species, dopant concentrations and createdefects.

Photolithographic patterning is necessary to define the areas across thesample to be selectively doped. This usually requires up to 10-15individual processing steps. Damage assisted sublimation etching (DASE)of Si and dopant out-diffusion are common problems observed during ionimplantation of SiC. Techniques allowing direct doping without therequirement for prepatterning can become economically viable [a) S. J.Pearton, Processing of Wide Bandgap Semiconductors, 1st Edition, WilliamAndrew Publishing, 2000; b) Z. C. Feng, J. H. Zhao, “Silicon Carbide:Materials, Processing, Devices”, Optoelectronic Properties ofSemiconductors and Superlattices, vol. 20, Taylor and Francis Books,Inc., 2004; c) M. E. Levinshtein et al, “Properties of AdvancedSemiconductor Materials”, Wiely-Interscience Publications, 2001].

U.S. Pat. No. 5,063,421 to Suzuki et al. discloses a silicon carbidelight emitting diode having a p-n junction is disclosed which comprisesa semiconductor substrate, a first silicon carbide single-crystal layerof one conductivity formed on the substrate, and a second siliconcarbide single-crystal layer of the opposite conductivity formed on thefirst silicon carbide layer, the first and second silicon carbide layersconstituting the p-n junction, wherein at least one of the first andsecond silicon carbide layers contains a tetravalent transition elementas a luminescent center.

U.S. Pat. No. 5,243,204 to Suzuki et al. discloses a silicon carbidelight emitting diodes having a p-n junction which is constituted by ap-type silicon carbide single-crystal layer and an n-type siliconcarbide single-crystal layer formed thereon. In cases where lightemission caused by recombination of free excitons is substantiallyutilized, at least a part of the n-type silicon carbide layer adjacentto the interface of the p-n junction is doped with a donor impurity at aconcentration of 5×10¹⁶ cm⁻³ or lower. In cases where light emissioncaused by acceptor-associated recombination is substantially utilized,the p-type silicon carbide layer is doped with an acceptor impurity andat least a part of the n-type silicon carbide layer adjacent to theinterface of the p-n junction is doped with a donor impurity at aconcentration of 1×10¹⁸ cm⁻³ or higher. Also provided are a method forproducing such silicon carbide light emitting diodes and a method forproducing another silicon carbide light emitting diode.

U.S. Pat. No. 5,416,342 to Edmond et al. discloses a light emittingdiode is disclosed that emits light in the blue portion of the visiblespectrum with high external quantum efficiency. The diode comprises asingle crystal silicon carbide substrate having a first conductivitytype, a first epitaxial layer of silicon carbide on the substrate andhaving the same conductivity type as the substrate, and a secondepitaxial layer of silicon carbide on the first epitaxial layer andhaving the opposite conductivity type from the first layer. The firstand second epitaxial layers forming a p-n junction, and the diodeincludes Ohmic contacts for applying a potential difference across thep-n junction. The second epitaxial layer has side walls and a topsurface that forms the top surface of the diode, and the secondepitaxial layer has a thickness sufficient to increase the solid angleat which light emitted by the junction will radiate externally from theside walls, but less than the thickness at which internal absorption insaid second layer would substantially reduce the light emitted from saidtop surface of the diode.

U.S. Pat. No. 6,900,465 to Nakamura et al. discloses a nitridesemiconductor light-emitting device has an active layer of asingle-quantum well structure or multi-quantum well made of a nitridesemiconductor containing indium and gallium. A first p-type clad layermade of a p-type nitride semiconductor containing aluminum and galliumis provided in contact with one surface of the active layer. A secondp-type clad layer made of a p-type nitride semiconductor containingaluminum and gallium is provided on the first p-type clad layer. Thesecond p-type clad layer has a larger band gap than that of the firstp-type clad layer. An n-type semiconductor layer is provided in contactwith the other surface of the active layer.

U.S. Pat. No. 6,998,690 to Nakamura et al discloses a galliumnitride-based III-V Group compound semiconductor device has a galliumnitride-based III-V Group compound semiconductor layer provided over asubstrate, and an Ohmic electrode provided in contact with thesemiconductor layer. The Ohmic electrode is formed of a metallicmaterial, and has been annealed.

U.S. Pat. No. 7,045,375 to Wu et al. discloses a white-light emittingdevice comprising a first PRS-LED and a second PRS-LED. The firstPRS-LED has a primary light source to emit blue light and a secondarylight source to emit red light responsive to the blue light; and thesecond PRS-LED has a primary light source to emit green light and asecondary light source for emitting red light responsive to the greenlight. Each of the primary light sources is made from an InGaN layerdisposed between a p-type GaN layer and an n-type GaN layer. Thesecondary light sources are made from AlGaInP. The primary light sourceand the secondary light source can be disposed on opposite sides of asapphire substrate. Alternatively, the second light source is disposedon the n-type GaN layer of the primary light source. The second lightsources may comprise micro-rods of AlGaInP of same or differentcompositions.

Discussion of wide bandgap materials and the processing thereof arediscussed in U.S. Pat. No. 5,145,741; U.S. Pat. No. 5,391,841; U.S. Pat.No. 5,793,042; U.S. Pat. No. 5,837,607; U.S. Pat. No. 6,025,609; U.S.Pat. No. 6,054,375; U.S. Pat. No. 6,271,576, U.S. Pat. No. 6,670,693,U.S. Pat. No. 6,930,009 and U.S. Pat. No. 6,939,748 are herebyincorporated by reference into the present application.

Therefore, it is an objective of this invention to provide a solid stateenergy conversion device and method of making a light emitting device toproduce electromagnetic radiation upon the application of electricalpower and/or a photovoltaic device to produce electrical power upon theapplication of electromagnetic radiation.

Another objective of this invention is to provide a solid state energyconversion device and method of making in a wide bandgap semiconductorfor enabling operation of the solid state energy conversion device atelevated temperatures.

Another objective of this invention is to provide a solid state energyconversion device and method of making that reduces the materials andlayers required to fabricate the solid state energy conversion devicethrough the fabrication of a monolithic structure.

Another objective of this invention is to provide a solid state energyconversion device and method of making that incorporates a process fordoping conventional and unconventional dopants in indirect wide bandgapsemiconductors to create efficient radiative states to provide anefficient solid state energy conversion device.

Another objective of this invention is to provide a solid state energyconversion device and method of making that incorporates combinations ofdopants which enables the tuning of solid state energy conversion deviceto a white light sensitivity of the solid state energy conversiondevice.

The foregoing has outlined some of the more pertinent objects of thepresent invention. These objects should be construed as being merelyillustrative of some of the more prominent features and applications ofthe invention. Many other beneficial results can be obtained bymodifying the invention within the scope of the invention. Accordinglyother objects in a full understanding of the invention may be had byreferring to the summary of the invention, the detailed descriptiondescribing the preferred embodiment in addition to the scope of theinvention defined by the claims taken in conjunction with theaccompanying drawings.

SUMMARY OF THE INVENTION

The present invention is defined by the appended claims with specificembodiments being shown in the attached drawings. For the purpose ofsummarizing the invention, the invention relates to a solid state energyconversion device and a method of making for converting energy betweenelectromagnetic and electrical energy. The solid state energy conversiondevice comprises a wide bandgap semiconductor material having a firstdoped region. A doping gas is applied to the first doped region of thewide bandgap semiconductor material. A thermal energy beam is directedonto the first doped region of the wide bandgap semiconductor materialin the presence of the doping gas for converting a portion of the firstdoped region into a second doped region in the wide bandgapsemiconductor material. A first and a second Ohmic contact are appliedto the first and the second doped regions of the wide bandgapsemiconductor material.

In a more specific embodiment of the invention, the step of providing awide bandgap semiconductor material having a first doped regioncomprises providing a wide bandgap semiconductor material selected fromthe group consisting of silicon carbide, gallium nitride, aluminumnitride, diamond, diamond like carbon, boron nitride and galliumphosphide.

In another specific embodiment of the invention, the step of applying adoping gas to the first doped region of the wide bandgap semiconductormaterial comprises applying a doping gas selected from the groupconsisting of nitrogen, trimethylaluminum, Bis(ethyl benzene)-chromium,diethylselenium and Eurpoium 2,2,6,6, Tetramethyl 3,5, heptanedionate.Preferably, the step applying of a doping gas to the first doped regionof the wide bandgap semiconductor material comprises applying a dopinggas containing a dopant atom having a valence sufficiently greater thatthe valence of the wide bandgap semiconductor material to provide amulti-hole donor within the first doped region of the wide bandgapsemiconductor material. In the alternative, the step applying of adoping gas to the first doped region of the wide bandgap semiconductormaterial comprises applying a doping gas containing a dopant atom havinga valence sufficiently less that the valence of the wide bandgapsemiconductor material to provide a multi-hole acceptor within the firstdoped region of the wide bandgap semiconductor material. The step ofapplying the first and second Ohmic contact may comprises applying thefirst and second Ohmic contact selected from the group consisting ofindium, aluminum and laser synthesized carbon rich conductor.

The solid state energy conversion device may operate as a light emittingdevice or a photovoltaic device. The solid state energy conversiondevice produces electromagnetic radiation upon the application ofelectrical power to the first and second Ohmic contacts to operate as alight emitting device. The solid state energy conversion device produceselectrical power between the first and second Ohmic contacts upon theapplication of electromagnetic radiation to operate as a photovoltaicdevice.

In another embodiment of the invention, the invention is incorporatedinto solid state energy conversion device comprising a wide bandgapsemiconductor material having a first doped region. A second dopedregion is formed in situ within a portion of the first doped region bydirecting a thermal energy beam onto the first doped region in thepresence of a doping gas for converting a portion of the first dopedregion into a second doped region. A first and a second Ohmic contact isconnected to the first and the second doped regions of the wide bandgapsemiconductor material. In one example, the solid state energyconversion device operates as a light emitting device to produceelectromagnetic radiation upon the application of electrical power tothe first and second Ohmic contacts. In another example, the solid stateenergy conversion device operates as a photovoltaic device to produceelectrical power between the first and second Ohmic contacts upon theapplication of electromagnetic radiation.

In still another embodiment of the invention, the invention isincorporated into the process of making a solid state light emittingdevice in a substrate of a wide bandgap semiconductor material. Theprocess comprises the steps of providing a wide bandgap semiconductormaterial having a first doped region. A doping gas is applied to thefirst doped region of the wide bandgap semiconductor material. A thermalenergy beam is directed onto the first doped region of the wide bandgapsemiconductor material in the presence of the doping gas for convertinga portion of the first doped region into a second doped region in thewide bandgap semiconductor material. A first and a second Ohmic contactis applied to the first and the second doped regions of the wide bandgapsemiconductor material. In one example, the solid state energyconversion device produces electromagnetic radiation upon theapplication of electrical power to the first and second Ohmic contactsto operate as a light emitting device having a color temperature that isbetween bright midday daylight and average daylight. In another example,the solid state energy conversion device produces electromagneticradiation upon the application of electrical power to the first andsecond Ohmic contacts to operate as a light emitting device having acolor temperature that is between bright midday daylight and averagedaylight.

In still another embodiment of the invention, the invention isincorporated into a solid state light emitting device comprising a widebandgap semiconductor material having a first doped region. A seconddoped region is formed in situ within a portion of the first dopedregion by directing a thermal energy beam onto the first doped region inthe presence of a doping gas for converting a portion of the first dopedregion into a second doped region. A first and a second Ohmic contactare connected to the first and the second doped regions of the widebandgap semiconductor material.

In a further embodiment of the invention, the invention is incorporatedinto a solid state photovoltaic device comprising a wide bandgapsemiconductor material having a first doped region. A second dopedregion is formed in situ within a portion of the first doped region bydirecting a thermal energy beam onto the first doped region in thepresence of a doping gas for converting a portion of the first dopedregion into a second doped region. A first and a second Ohmic contactare connected to the first and the second doped regions of the widebandgap semiconductor material.

The foregoing has outlined rather broadly the more pertinent andimportant features of the present invention in order that the detaileddescription that follows may be better understood so that the presentcontribution to the art can be more fully appreciated. Additionalfeatures of the invention will be described hereinafter which form thesubject of the claims of the invention. It should be appreciated bythose skilled in the art that the conception and the specificembodiments disclosed may be readily utilized as a basis for modifyingor designing other structures for carrying out the same purposes of thepresent invention. It should also be realized by those skilled in theart that such equivalent constructions do not depart from the spirit andscope of the invention as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and objects of the invention,reference should be made to the following detailed description taken inconnection with the accompanying drawings in which:

FIG. 1 is a side view of an air-tight chamber with a thermal energy beamimpinging on a wide-bandgap semiconductor substrate for forming a solidstate energy conversion device of the present invention;

FIG. 2 is an enlarged isometric view of the substrate of FIG. 1;

FIG. 3A is a side sectional view of a first example of a solid stateenergy conversion device formed in accordance with the present inventionto provide a solid state light emitting device;

FIG. 3B is a side sectional view of a second example of a solid stateenergy conversion device formed in accordance with the present inventionto provide a solid state light emitting device;

FIG. 3C is a side sectional view of a third example of a solid stateenergy conversion device formed in accordance with the present inventionto provide a solid state light emitting device;

FIG. 4A is a side sectional view of a fourth example of a solid stateenergy conversion device formed in accordance with the present inventionto provide a solid state photovoltaic device;

FIG. 4B is a side sectional view of a fifth example of a solid stateenergy conversion device formed in accordance with the present inventionto provide a solid state photovoltaic device;

FIG. 4C is a side sectional view of a sixth example of a solid stateenergy conversion device formed in accordance with the present inventionto provide a solid state photovoltaic device;

FIG. 5 is a graph of conventional dopant diffusivity in SiC as afunction of reciprocal temperature for conventional processing.

FIG. 6 is a graph of concentration of the dopants Cr, N and Al as afunction of depth within a 6H—SiC silicon carbide wide bandgapsubstrate;

FIG. 7 is a graph of concentration of the dopants Cr, N and Al as afunction of depth within a 4H—SiC silicon carbide wide bandgapsubstrate;

FIG. 8A is a side sectional view of a first example of a white lightsolid state emitting device fabricated on 6H:SiC (n-type) substrate bydoping with aluminum and chromium;

FIG. 8B is a graph of light intensity as a function of wavelength forthe solid state light emitting device of FIG. 8A;

FIG. 9A is a side sectional view of a second example of a white lightsolid state light emitting device fabricated on 4H:SiC (p-type)substrate by doping with nitrogen and chromium;

FIG. 9B is a graph of light intensity as a function of wavelength forthe solid state light emitting device of FIG. 9A;

FIG. 10A is a side sectional view of a third example of an orange-redsolid state light emitting device fabricated on 4H:SiC (p-type)substrate by doping with chromium;

FIG. 10B is a graph of light intensity as a function of wavelength forthe solid state light emitting device of FIG. 10A;

FIG. 11A is a side sectional view of a fourth example of a green lightsolid state light emitting device fabricated on 6H:SiC (n-type)substrate by doping with chromium;

FIG. 11B is a graph of light intensity as a function of wavelength forthe solid state light emitting device of FIG. 11A;

FIG. 12A is a side sectional view of a fifth example of a red lightsolid state light emitting device of fabricated on 4H:SiC (n-type)substrate by doping with chromium;

FIG. 12B is a graph of light intensity as a function of wavelength forthe solid state light emitting device of FIG. 12A;

FIG. 13A is a side sectional view of a sixth example of a blue lightsolid state light emitting device fabricated on 6H:SiC (n-type)substrate by doping with aluminum;

FIG. 13B is a graph of light intensity as a function of wavelength forthe solid state light emitting device of FIG. 13A;

FIG. 14A is a side sectional view of a seventh example of a blue-greensolid state light emitting device fabricated on 6H:SiC (n-type)substrate by doping with boron; and

FIG. 14B is a graph of light intensity as a function of wavelength forthe solid state light emitting device of FIG. 14A; and

FIG. 15 is a graph of operational temperature as a function of band gapfor various solid sate devices; and

FIG. 16 is a side sectional view of a solid state photovoltaic devicefabricated on 6H:SiC (n-type) substrate by doping with aluminum andchromium.

Similar reference characters refer to similar parts throughout theseveral Figures of the drawings.

DETAILED DISCUSSION

FIG. 1 is a side view of an apparatus 5 for forming a solid state energyconversion device 10 on a wide-bandgap semiconductor substrate 20. Thewide-bandgap semiconductor substrate 20 is shown located in an air-tightchamber 30. The chamber 30 has an inlet valve combination 31 and outletvalve 32 connected to the side wall of the chamber 30 for injecting andremoving gases into and out of the chamber 30, respectively. The chamber30 includes an airtight transmission window 34. The chamber 30 isdisposed on a support member 36 forming an airtight seal therewith.

FIG. 2 is an enlarged isometric view of the solid state energyconversion device 10 formed in situ within the wide-bandgapsemiconductor substrate 20 shown in FIG. 1. The wide-bandgapsemiconductor substrate 20 defines a first and a second side 21 and 22and a peripheral edge 23. Although the wide-bandgap semiconductorsubstrate 20 is shown as a square, the present invention is not limitedby the physical configuration of the wide-bandgap semiconductorsubstrate 20 as shown herein.

Preferably, the wide-bandgap semiconductor 20 has a bandgap greater than2.0 electron volts. In one example, the wide-bandgap semiconductor 20 isselected from the group IV of the periodic table and having a bandgapgreater than 2.0 electron volts. In a more specific example of theinvention, the wide-bandgap semiconductor 20 is essentially a singlecrystal structure.

In still a more specific example of the invention, the wide-bandgapsemiconductor 20 may be a single crystal compound. The elements of thesingle crystal compound selected are from the group III, the group IVand the group V of the periodic table and having bandgap greater than2.0 electron volts. Preferably, one element of the compound has a highermelting point element than the other element of the compound. Specificexamples of the wide-bandgap semiconductor compound are selected fromthe group consisting of Aluminum Nitride, Silicon Carbide, BoronNitride, Gallium Nitride, diamond, diamond like carbon (DLC) and GalliumPhosphide.

A thermal energy beam 40 is shown emanating from a source 42 and passingthrough the airtight transmission window 34 to impinge on the firstsurface 21 of the wide-bandgap semiconductor substrate 20. In oneexample, the thermal energy beam 40 is a beam of charged particles suchas a beam of electrons or a beam of ions. In another example, thethermal energy beam 40 is a beam of electromagnetic radiation such as alaser beam. Examples of a suitable source of the laser beam include aNd:YAG laser, a frequency double 2ω Nd:YAG laser or an Excimer laser.

The thermal energy beam 40 is scanned in two dimensions across the firstsurface 21 of the wideband gap semiconductor substrate 20 to form thesolid state energy conversion device 10. In this example, the firstsurface 11 of the solid state energy conversion device 10 is coincidentwith the first surface 21 of the wideband gap semiconductor substrate 20with the remainder of the solid state energy conversion device 10including the second surface 12 and the peripheral surface 13 beingembedded within the wideband gap semiconductor substrate 20.

The thermal energy beam 40 impinges on the wide-bandgap semiconductorsubstrate 20 to create the solid state energy conversion device 10within the wide-bandgap semiconductor substrate 20. In this example, thesolid state energy conversion device 10 is located on the first side 21of the wide-bandgap semiconductor substrate 20. The solid state energyconversion device 10 is shown as a portion of the wide-bandgapsemiconductor substrate 20 formed by causing relative movement betweenthe wide-bandgap semiconductor substrate 20 and the thermal energy beam40.

The wide-bandgap semiconductor substrate 20 may be formed as a monolithor a thin film substrate having suitable properties for forming thesolid state energy conversion device 10 in the wide-bandgapsemiconductor substrate 20. Laser doping can be conducted on opposingsurfaces of a substrate, wafer, thin film, thin film deposited on aflexible substrate or in different regions on the same surface.

Table 1 sets the initial properties of a wide-bandgap semiconductorsubstrate 20 suitable for creating the solid state energy conversiondevice 10 of the present invention.

TABLE 1 Properties of Parent Substrates for SiC Energy Conversion DeviceFabrication Typical principle Typical dopant Parent ResistivityPrinciple concentration Substrate (ohm-cm) Dopant (/cc) Notes: 6H—SiC n-0.05  Nitrogen   10¹⁶ a) acceptor type impurities may be present b)defects can behave as acceptors 6H—SiC p- 0.1-0.2 Aluminum 10¹⁷-10²⁰ a)Nitrogen type (donor) impurities may be present. b) defects can behaveas donors 6H—SiC 10⁶-10¹¹ Vanadium <10¹⁴ a) Vanadium can semi- behave asa donor insulating or acceptor. b) Vanadium can complex with defectscreating local strains, which create local dipoles which behave aselectron carriers. c) Nitrogen can be on the order of 10¹⁶/cc 4H—SiC n-0.044 Nitrogen   10¹⁶ a) acceptor type impurities may be present b)defects can behave as acceptors 4H—SiC p- 0.1-0.2 Aluminum 10¹⁷-10²⁰ a)Nitrogen type (donor) impurities may be present. b) point defects canbehave as donors 4H—SiC 10⁹-10¹¹ Vanadium <10¹⁴ a) Vanadium can semi-behave as a insulating donor or acceptor; b) Vanadium can complex withdefects creating local strains, which create local dipoles which behaveas electron carriers. c) Nitrogen can be on the order of 10¹⁶/cc

Wide bandgap semiconductors (WBGSs) have been laser doped with both n-and p-type dopants. Specific dopant types and substrates includenitrogen and cobalt in diamond-like carbon; magnesium in GaN; andaluminum, nitrogen, chromium, boron, gallium, europium, erbium,selenium, oxygen and thulium in silicon carbide from metal-organic andpowder precursors.

Laser doping achieves higher dopant concentration than by conventionalion implantation doping. Nitrogen dopant concentration is increased oneto three orders of magnitude while aluminum doping is increased from oneto four orders of magnitude compared to ion implantation withoutcreating lattice defects. Laser doping depths can be 200-300 nm up to 4microns or greater. Laser doping enables the doping of atoms, frompreferably a metal-organic precursor, that have a valence greater thanthe positive valence atom in the parent substrate. These unconventionaldopants contribute multiple holes per atom creating more efficientradiative states in indirect wide bandgap semiconductors.

For n-type doping, the sample was placed in nitrogen atmosphere atpressure of 30 psi and laser-doped regions were formed on the samplesurface by moving the chamber with a stepper motor-controlledtranslation stage. The height of the chamber was controlled manuallythrough an intermediate stage to obtain different laser spot sizes onthe SiC substrate. In case of gallium phosphide (GaP), nitrogen acts asan iso-electronic defect rather than a n-type dopant. For p-type doping,TMA (trimethylaluminum, (CH3)3Al), Bis(ethyl benzene)-chromium and boronwere used. TMA was heated in a bubbler source immersed in a water bathmaintained at 70° C. until it evaporated and then a carrier gas,methane, was passed through the bubbler to transport the TMA vapor tothe laser doping chamber. Similarly for chromium doping, Bis(ethylbenzene)-chromium was heated in a bubbler source immersed in a waterbath maintained at 100° C. until it evaporated and then a carrier gas,argon, was passed through the bubbler to transport the ethyl benzenechromium vapor to the laser doping chamber. These dopant gas speciesdecompose at the laser-heated substrate surface producing Al and Cratoms, which subsequently diffuse into the substrate.

A more detailed discussion follows on the importance doping with atomsthat have a sufficient valence to create multi-hole acceptors. Chromium(6+), which has a valence of two greater than the silicon (4+) componentof silicon carbide, is used as a dopant example to create efficientradiative states. Normally dopant atoms are from the adjacent groups inthe periodic table that are on either side of the atom of an atomicconstituent of the parent wide bandgap semiconductor. For example Si isin group IV and elements such as Al (p-type dopant) and P (n-typedopant) are in groups III and V respectively. The transition metal Crhas been doped into SiC, which does not follow this conventionalapproach. Additionally Cr acts as an acceptor creating two holes per Cratom (a multi-hole acceptor); higher Cr concentrations greatly increasethe acceptor population as confirmed by deep level transientspectroscopy (DLTS). DLTS spectra of a 4H—SiC (n-type-N) wafer substratelaser doped with chromium shows minority carrier trap peaks due toacceptor (holes) states in a chromium-doped 4H—SiC (n-type) wafer, whichconfirms that chromium is a p-type dopant. The DLTS technique is apowerful tool for determining the defect properties such as defectenergy level, capture cross-section, and trap density. A modified DLTSthat combines junction spectroscopy with illumination in a double pulseapproach can be used to identify the minority carrier traps acting asrecombination centers.

The technique is based on the transient capacitance change associatedwith the thermal emission of charge carriers from a trap level tothermal equilibrium after an initial non-equilibrium condition in thespace-charge region of a Schottky barrier or a p-n junction diode. Thepolarity of the DLTS peak depends on the capacitance change aftertrapping the minority or majority carriers. In general, a minoritycarrier trap produces a positive DLTS peak, while a majority carriertrap yields a negative DLTS peak. [D. V. Lang, Fast capacitancetransient apparatus: Application to ZnO and O centers in GaP p-njunctions, J. Appl. Phys. 45 (1974) 3014-3022.

The active state of Cr was confirmed by Hall effect measurements using aCr-doped n-type (nitrogen-doped) 4H—SiC sample. This sample was preparedusing the same laser doping parameters as used for laser doping Cr intothe p-type 4H—SiC wafer. The Hall measurement identified the Cr-dopedregion as p-type with a carrier concentration of 1.942×10¹⁹ cm⁻³ whichis almost twice the average dopant concentration (˜10¹⁹ cm⁻³). Theaverage dopant concentration is based on the Secondary Ion MassSpectroscopy (SIMS) data for n-type 4H—SiC with a concentration of2×10¹⁹ cm³ at the wafer surface and 10¹⁷ cm⁻³ at a depth of 500 nm. Thisdata confirms Cr as a double acceptor and also indicate that the laserdoping technique activated all the dopant atoms without the need of anyadditional annealing step.

Conversely, SiC can be doped with fewer Cr atoms than Al atoms toachieve the same hole concentration. Fewer Cr atoms in the SiC latticeis expected to produce less strain and defects in the material than inthe case of higher concentrations of Al.

Similarly, multi-electron donors can be laser doped into SiC. Europiumhaving a +2 valence, derived from a Europium Tetramethyl, 3,5heptanedionate precursor vapor decomposes upon laser heating and isdiffused into SiC substrate using the process described for Cr laserdoping. Selenium derived from a diethylselenium precursor also behavesas a multi-electron donor.

Laser doping can convert indirect bandgap semiconductors to directbandgap semiconductors by intentionally inducing strain to alterelectron momentum states. An indirect bandgap semiconductor has aconduction band bottom that does not occur at momentum (k)=0 while thetop of the valence band does occur at k=0. Therefore energy releasedduring electron recombination with a hole is converted primarily into aphonon (additional momentum), a quasi-particle which is a quantizedsound wave; e.g. Si, GaP, SiC. A direct bandgap semiconductor has aconduction band bottom and valence band top occurring at the momentumk=0. Therefore energy released during band-to-band electronrecombination with a hole is converted primarily into photon radiation(radiant recombination) exhibiting a wavelength determined by the energygap; e.g. GaAs, InP, GaN; no extra momentum is required. Direct bandgapsemiconductors are sometimes referred to as “optically active” andindirect as “optically inactive”. Laser doping where the dopant has avalence greater than the highest valence atom of the comprising theparent wide bandgap semiconductor can transform the SiC indirect widebandgap semiconductor into a direct bandgap semiconductor; dopants witha valence 2 or greater than the highest valence atom comprising theparent wide bandgap semiconductor are preferred. This doping inducesstrain which alters the momentum state of the electrons and facilitatesthe transfer of electron-hole recombination between the conduction andvalence bands with no additional momentum.

Conversely a solid state photovoltaic device with p and n regions canproduce electric current when light or electromagnetic radiation isirradiated on the solid state photovoltaic device.

The laser doping technology of the present invention can be used tocreate energy conversion devices in many semiconductor structures suchas diodes, transistors and other electron components in monolithic orthin film geometries.

FIG. 3A is a side sectional view of a first example of a solid stateenergy conversion device 10A formed in accordance with the presentinvention to provide a solid state light emitting device. In thisexample, the substrate 20A has a first and a second side 21A and 22A anda peripheral edge 23A. A laser doped region 51A is formed on the firstside 21A of the substrate 20A. A first and a second Ohmic contact 61Aand 62A are electrically connected to the first and second side 21A and22A of the substrate 20A. The solid state light emitting device 10Aproduces electromagnetic radiation when an electric current is injectedbetween the first and second Ohmic contacts 61N and 62N as indicated bythe battery 71A.

Preferably, the first and second electrodes 61A and 62A are formed bythe thermal conversion of the wide-bandgap semiconductor substrate 20A.The conversion of the portions of the wide-bandgap semiconductorsubstrate 20A to provide the first and second electrodes 61A and 62A isset forth in my U.S. Pat. No. 5,145,741; U.S. Pat. No. 5,391,841; U.S.Pat. No. 5,793,042; U.S. Pat. No. 5,837,607; U.S. Pat. No. 6,025,609;U.S. Pat. No. 6,054,375; U.S. Pat. No. 6,271,576 and U.S. Pat. No.6,670,693.

FIG. 3B is a side sectional view of a second example of a solid stateenergy conversion device formed in accordance with the present inventionto provide a solid state light emitting device 10B. In this example, thesubstrate 20B has a first and a second side 21B and 22B and a peripheraledge 23B. Laser doped regions 51B and 52B are formed on the first side21B of the substrate 20A. A first and a second Ohmic contact 61B and 62Bare electrically connected to the laser doped regions 51B and 52B. Thesolid state light emitting device 10B produces electromagnetic radiationwhen an electric current is injected between the first and second Ohmiccontacts 61B and 62B as indicated by the battery 71B.

FIG. 3C is a side sectional view of a third example of a solid stateenergy conversion device formed in accordance with the present inventionto provide a solid state light emitting device 10C. In this example, thesubstrate 20C has a first and a second side 21C and 22C and a peripheraledge 23C. Laser doped regions 51C and 52C are formed in layers on thefirst side 21C of the substrate 20A. A first and a second Ohmic contact61A and 62A are electrically connected to the first and second side 21Cand 22C of the substrate 20C. The solid state light emitting device 10Cproduces electromagnetic radiation when an electric current is injectedbetween the first and second Ohmic contacts 61C and 62C as indicated bythe battery 71C.

FIG. 4A is a side sectional view of a fourth example of a solid stateenergy conversion device formed in accordance with the present inventionto provide a solid state photovoltaic device 10D. In this example, thesubstrate 20D has a first and a second side 21D and 22D and a peripheraledge 23D. A laser doped region 51D is formed on the first side 21D ofthe substrate 20D. A first and a second Ohmic contact 61D and 62D areelectrically connected to the first and second side 21D and 22D of thesubstrate 20D. The solid state photovoltaic device 10D produces anelectric current between the first and second Ohmic contacts 61D and 62Dupon receiving electromagnetic radiation as indicated by the ammeter72D.

FIG. 4B is a side sectional view of a fifth example of a solid stateenergy conversion device formed in accordance with the present inventionto provide a solid state photovoltaic device 10E. In this example, thesubstrate 20E has a first and a second side 21E and 22E and a peripheraledge 23E. Laser doped regions 51E and 52E are formed in the first andsecond sides 21E and 22E of the substrate 20E. A first and a secondOhmic contact 61E and 62E are electrically connected to the first andsecond side 21E and 22E of the substrate 20E. The solid statephotovoltaic device 10E produces an electric current between the firstand second Ohmic contacts 61E and 62E upon receiving electromagneticradiation as indicated by the ammeter 72E.

FIG. 4C is a side sectional view of a sixth example of a solid stateenergy conversion device formed in accordance with the present inventionto provide a solid state photovoltaic device 10F. In this example, thesubstrate 20F has a first and a second side 21F and 22F and a peripheraledge 23F. Laser doped regions 51F and 52F are formed in layers on thefirst side 21F of the substrate 20F. A first and a second Ohmic contact61F and 62F are electrically connected to the first and second side 21Fand 22F of the substrate 20F. The solid state photovoltaic device 10Fproduces an electric current between the first and second Ohmic contacts61F and 62F upon receiving electromagnetic radiation as indicated by theammeter 72F.

FIG. 5 is a graph of diffusivity of various conventional dopants intoSiC using conventional doping processes (e.g., thermal, ionimplantation). Conventional doping processes also limit the choice ofdopants. For example, nitrogen diffusivity in silicon carbide SiC is5×10¹² cm²/second at a temperature greater than 2500° C. and aluminumdiffusivity in silicon carbide SiC is 3×10⁻¹⁴ to 6×10¹² cm²/second at atemperature greater than 1200° C. using conventional doping techniques.The process of laser doping of the present invention increases nitrogendiffusivity in silicon carbide SiC between 2×10⁻⁵ and 9×10⁻⁶ cm²/sec andincreases aluminum diffusivity in silicon carbide SiC between 1×10⁻⁵ and1×10⁻⁶ cm²/sec. The process of laser doping of the present inventionenables the use of new species of dopants including chromium (Cr),europium (Eu) and selenium (Se) with wide bandgap substrates.

Laser doping, a non-equilibrium process, enables achievement of veryhigh dopant concentrations at the surface, which can exceed thesolubility limit. Z. Tian, N. R. Quick and A. Kar, Acta Materialia, 54,4273, (2006) have shown that laser doping enhances the diffusioncoefficient of aluminum and nitrogen in SiC by about six orders ofmagnitude when compared to conventional doping techniques. It readilyfacilitates the formation of dopant concentration gradients along thedepth of the wafer, i.e., the concentration decreases gradually alongthe depth. A linearly graded junction can be obtained that furtherfacilitates the effective electron-hole recombination within thedepletion region for light emitting applications, E. Fred Schubert,“Light Emitting Diodes”, Cambridge University Press, (2003).

A PHI Adept 1010 Dynamic Secondary Ion Mass Spectroscopy system (SIMS)was used to determine the dopant concentration and its variation alongthe depth for the p and n regions of the device. An aluminum-doped SiCstandard (1×10¹⁹ cm-3), Cr-implanted SiC standard (1×10²⁰ cm⁻³), N-dopedSiC standard (5×10¹⁸ cm⁻³), as received 4H—SiC (p-type) and anas-received 6H—SiC (n-type) (5×10¹⁸ cm⁻³) were also analyzed forreference and background concentrations

FIG. 6A is a graph of concentration of the dopants Cr, N and Al as afunction of depth within a 6H—SiC silicon carbide wide bandgap substrate20. In case of a 6H—SiC silicon carbide wide bandgap substrate 20, avery high concentration of about 2×10²⁰ cm⁻³ was measured for Al at thesurface decreasing gradually to 1×10¹⁸ cm⁻³ to a depth of 700 nm, whilea concentration of 1×10¹⁹ cm⁻³ was measured for Cr at the surfacedecreasing gradually to the background concentration of 1×10¹⁷ cm⁻³ at adepth of 420 nm. The penetration depth of Al is much larger than that ofCr due to the size effect of these elements. Aluminum is much smallerthan Cr and slightly smaller than Si and it can penetrate SiC easily andoccupy the available Si vacancies. For Cr occupancy of Si vacancies thepenetration is accompanied by lattice strain. Additionally, the solidsolubility limits in SiC for Al (2×10²¹ cm⁻³) is much higher than Cr(3×10¹⁷ cm⁻³) G. L. Harris, “Properties of silicon carbide”, IEE Inspecpublication, emis data review series 13, (1995).

The concentration of Cr at the surface is about two orders of magnitudehigher than the solid solubility limit, while for aluminum it is veryclose to the solubility limit.

FIG. 6B is a graph of concentration of the dopants Cr, N and Al as afunction of depth within a 4H—SiC silicon carbide wide bandgap substrate20. In case of a 4H—SiC silicon carbide wide bandgap substrate 20, avery high concentration of approximately 1×10²¹ cm⁻³ was obtained for Nat the surface decreasing gradually to 3×10¹⁷ cm⁻³ to a depth of 8.5 μm,while a concentration of 1.5×10¹⁹ cm-3 was obtained for Cr at thesurface decreasing gradually to the background concentration of 1×10¹⁵cm⁻³ at a depth of 80 nm. The penetration depth of N is much larger thanthat of Cr, which results from the atomic radius difference. The smallernitrogen atom can penetrate SiC easily and occupy the available C or Sivacancies. Also, the solid solubility limits in SiC for N (6×10²⁰ cm⁻³)is much higher than Cr (3×10¹⁷ cm⁻³). These dopant concentration levelsand their penetration depths can be altered easily by modifying thedoping parameters. Laser doping thus provides this advantage and iscompatible with both conventional (e.g., Al, N) and unconventional(e.g., Cr) dopants.

FIG. 7 is a graph of operating temperature as a function of bandgap forvarious types of p-n junctions semiconductors. Since crystalline SiC ischemically inert and has good thermo-mechanical properties at hightemperatures, photovoltaic device made of p-n regions in SiC can belocated at the walls of combustion chambers, particularly in powerplants, to directly convert radiative energy, e.g., heat, intoelectrical energy. Burning fuels and the resultant flames produceelectromagnetic radiation in the ultraviolet (UV), visible and infraredregions of the spectrum. The combustion chamber is modified to containstacks of SiC photovoltaic cells so that each stack can absorb theradiation of a selected wavelength range to directly produceelectricity.

Light Emitting Device

FIG. 8A is a side sectional view of a first example of a light emittingdevice 10G fabricated on 6H:SiC (n-type) substrate 20G by doping withaluminum and chromium. The substrate 20G defines a first and a secondside 21G and 22G and a peripheral edge 23G. A first and a second Ohmiccontact 61G and 62G are electrically connected to the first and secondside 21G and 22G of the substrate 20G.

Table 2 sets forth the parameters for the fabrication of the lightemitting device 10G of FIG. 8A. It should be appreciated by thoseskilled in the art that Table 2 is a specific example and that numerousother parameters may be used to fabricate light emitting devices havingdifferent characteristics.

TABLE 2 Pulse Color repetition Focal Spot Scanning Contribution Powerrate Length size # of speed Dopant Sample in LEDs Dopant (W) (KHz) (mm)(μm) passes (mm/sec) medium 6H:SiC White, Cr 11.6 4 150 65 1 0.8 Bis(ethyl n-type Green benzene)- chromium, argon 30 psi White, Blue Al11.5-12 5 150 65 2 0.5 Trimethyl aluminum, Methane 30 psi

FIG. 8B is a graph of light intensity as a function of wavelength forthe light emitting device 10G of FIG. 8A. The graph of FIG. 8Billustrates the distribution of light intensity, in arbitrary units, asa function of frequency for the light emitting device 10G of FIG. 8A.The sum of the distribution of light intensity of the light emittingdevice 10G results in a white light. The white light emission is createdby laser doping with aluminum and chromium. A broad EL spectrum startingfrom 400 nm (band gap of 6H—SiC) to 900 nm covering the entire visiblespectrum is observed. The red luminescence results form a nitrogenexcitation and other defect states luminescence. The green and blueluminescence result from donor-acceptor pair recombination between N—Crand N—Al, respectively. This red-green-blue (RGB) combination producesan observed broadband white light.

Current LED technology has shortcomings with matching color renderingindex and color temperature of sunlight. The color rendering index (CRI)(sometimes called Color Rendition Index), is a measure of the ability ofa light source to reproduce the colors of various objects being lit bythe source. It is a method devised by the International Commission onIllumination (CIE). The human eye has receptors for short (S), middle(M), and long (L) wavelengths, also known as blue, green, and redreceptors. That means that one, in principle, needs three parameters todescribe a color sensation. A specific method for associating threenumbers (or tristimulus values) with each color is called a color space,of which the CIE XYZ color space is one of many such spaces. However,the CIE XYZ color space is special, because it is based on directmeasurements of the human eye, and serves as the basis from which manyother color spaces are defined.

In the CIE XYZ color space, the tristimulus values are not the S, M, andL stimuli of the human eye, but rather a set of tristimulus valuescalled X, Y, and Z, which are also roughly red, green and blue,respectively. Two light sources may be made up of different mixtures ofvarious colors, and yet have the same color (metamerism). If two lightsources have the same apparent color, then they will have the sametristimulus values, no matter what different mixtures of light were usedto produce them.

“Visible light” is commonly described by its color temperature. Atraditional incandescent light source's color temperature is determinedby comparing its hue with a theoretical, heated black-body radiator. Anincandescent light is very close to being a black-body radiator.However, many other light sources, such as fluorescent lamps, do notemit radiation in the form of a black-body curve, and are assigned whatis known as a correlated color temperature (CCT), which is the colortemperature of a black body which most closely matches the lamp'sperceived color. Because such an approximation is not required forincandescent light, the CCT for an incandescent light is simply itsunadjusted kelvin value, derived from the comparison to a heatedblack-body radiator. Bright midday sun is 5200 K and average daylight,and electronic flash, is 5500K.

The color rendering index of the white light emitting diode as per the1931 CIE chromaticity at 2 degree on 6H—SiC (n-type-N) wafer substratelaser doped with aluminum and chromium has the following tristimulusvalues; X=0.3362, Y=0.3424 and Z=0.3214 which confirms white colorspace. These values render a color temperature of 5338 K which is veryclose to the incandescent lamp (or black body) and lies between brightmidday sun (5200 K) and average daylight (5500 K)

FIG. 9A is a side sectional view of a first example of a light emittingdevice 10H fabricated on 4H:SiC (p-type) substrate 20H by doping with awith nitrogen and chromium. The substrate 20H defines a first and asecond side 21H and 22H and a peripheral edge 23H. A first and a secondOhmic contact 61H and 62H are electrically connected to the first andsecond side 21H and 22H of the substrate 20H.

Table 3 sets forth the parameters for the fabrication of the lightemitting device 10H of FIG. 9A. It should be appreciated by thoseskilled in the art that Table 3 is a specific example and that numerousother parameters may be used to fabricate light emitting devices havingdifferent characteristics.

TABLE 3 Pulse Color repetition Focal Spot Scanning Contribution Powerrate Length size # of speed Dopant Sample in LEDs Dopant (W) (KHz) (mm)(μm) passes (mm/sec) medium 4H:SiC White N 12 5 150 80 3 0.8 Ultra highpure p-type nitrogen 30 psi White, Cr 12.5-13 5 150 65 1 0.5 Bis (ethylOrange-Red benzene)- chromium, argon 30 psi

FIG. 9B is a graph of light intensity as a function of wavelength forthe light emitting device 10H of FIG. 9A. The graph of FIG. 9Billustrates the distribution of light intensity as a function offrequency for the light emitting device 10H of FIG. 9A. The sum of thedistribution of light intensity of the light emitting device 10H resultsin a white light. White light emission is created by laser doping withboth nitrogen and chromium. A broad spectrum extending from 380 nm (bandgap of 4H—SiC) to 850 nm is observed. Green and blue wavelengths areobserved due to the occurrence of radiative recombination transitionsbetween donor-acceptors pairs of N—Cr and N—Al respectively, whileprominent violet wavelength was observed due to nitrogen-valence bandlevel transitions. The red luminescence was mainly due to nitrogenexciton and other defect levels. This red-green-blue (RGB) combinationproduces an observed broadband white light. The color rendering indexfor this white light emitting diode as per the 1931 CIE chromaticity at2 degree has the following tristimulus values; X=0.3322, Y=0.3320 andZ=0.3358. The color temperature is 5510 K which is very close to averagedaylight (5500 K)

FIG. 10A is a side sectional view of a first example of a light emittingdevice 10I fabricated on 4H:SiC (p-type) substrate 20I by doping withchromium. The substrate 20I defines a first and a second side 21I and22I and a peripheral edge 23I. A first and a second Ohmic contact 61Iand 62I are electrically connected to the first and second side 21I and22I of the substrate 20I.

Table 4 sets forth the parameters for the fabrication of the lightemitting device 10I of FIG. 7A. It should be appreciated by thoseskilled in the art that Table 4 is a specific example and that numerousother parameters may be used to fabricate light emitting devices havingdifferent characteristics.

TABLE 4 Pulse Color repetition Focal Spot Scanning Contribution Powerrate Length size # of speed Dopant Sample in LEDs Dopant (W) (KHz) (mm)(μm) passes (mm/sec) medium 4H:SiC White, Cr 12.5-13 5 150 65 1 0.5 Bis(ethyl p-type Orange-Red benzene)- chromium, argon 30 psi

FIG. 10B is a graph of light intensity as a function of wavelength forthe light emitting device 10I of FIG. 10A. The graph of FIG. 10Billustrates the distribution of light intensity as a function offrequency for the light emitting device 10I of FIG. 10A. The sum of thedistribution of light intensity of the light emitting device 10I resultsin an orange-red light.

FIG. 11A is a side sectional view of a first example of a light emittingdevice 10J fabricated on 6H:SiC (n-type) substrate 20J by doping withchromium. The substrate 20J defines a first and a second side 21J and22J and a peripheral edge 23J. A first and a second Ohmic contacts 61Jand 62J are electrically connected to the first and second side 21J and22J of the substrate 20J.

Table 5 sets forth the parameters for the fabrication of the lightemitting device 10J of FIG. 11A. It should be appreciated by thoseskilled in the art that Table 5 is a specific example and that numerousother parameters may be used to fabricate light emitting devices havingdifferent characteristics.

TABLE 5 Pulse Color repetition Focal Spot Scanning Contribution Powerrate Length size # of speed Dopant Sample in LEDs Dopant (W) (KHz) (mm)(μm) passes (mm/sec) medium 6H:SiC White, Cr 11.6 4 150 65 1 0.8 Bis(ethyl n-type Green benzene)- chromium, argon 30 psi

FIG. 11B is a graph of light intensity as a function of wavelength forthe light emitting device 10J of FIG. 11A. The graph of FIG. 11Billustrates the distribution of light intensity as a function offrequency for the light emitting device 10J of FIG. 11A. The sum of thedistribution of light intensity of the light emitting device 10J resultsin a green light.

FIG. 12A is a side sectional view of a first example of a light emittingdevice 10K fabricated on 4H:SiC (n-type) substrate 20K by doping withchromium. The substrate 20K defines a first and a second side 21K and22K and a peripheral edge 23K. A first and a second Ohmic contact 61Kand 62K are electrically connected to the first and second side 21K and22K of the substrate 20K.

Table 6 sets forth the parameters for the fabrication of the lightemitting device 10K of FIG. 12A. It should be appreciated by thoseskilled in the art that Table 6 is a specific example and that numerousother parameters may be used to fabricate light emitting devices havingdifferent characteristics.

TABLE 6 Pulse Color repetition Focal Spot Scanning Contribution Powerrate Length size # of speed Dopant Sample in LEDs Dopant (W) (KHz) (mm)(μm) passes (mm/sec) medium 4H:SiC White, Red, Cr 12 5 150 65 2 0.5 Bis(ethyl n-type Green, benzene)- Voilet chromium, argon 30 psi

FIG. 12B is a graph of light intensity as a function of wavelength forthe light emitting device 10K of FIG. 12A. The graph of FIG. 12Billustrates the distribution of light intensity as a function offrequency for the light emitting device 10K of FIG. 12A. The sum of thedistribution of light intensity of the light emitting device 10K resultsin a red light.

FIG. 13A is a side sectional view of a first example of a light emittingdevice 10L fabricated on 6H:SiC (n-type) substrate 20L by doping withaluminum. The substrate 20L defines a first and a second side 21L and22L and a peripheral edge 23L. A first and a second Ohmic contact 61Land 62L are electrically connected to the first and second side 21L and22L of the substrate 20L.

Table 7 sets forth the parameters for the fabrication of the lightemitting device 10L of FIG. 13A. It should be appreciated by thoseskilled in the art that Table 7 is a specific example and that numerousother parameters may be used to fabricate light emitting devices havingdifferent characteristics.

TABLE 7 Pulse Color repetition Focal Spot Scanning Contribution Powerrate Length size # of speed Dopant Sample in LEDs Dopant (W) (KHz) (mm)(μm) passes (mm/sec) medium 6H:SiC White, Blue Al 11.5-12 5 150 65 2 0.5Trimethyl n-type aluminum, Methane 30 psi

FIG. 13B is a graph of light intensity as a function of wavelength forthe light emitting device 10L of FIG. 13A. The graph of FIG. 13Billustrates the distribution of light intensity as a function offrequency for the light emitting device 10L of FIG. 13A. The sum of thedistribution of light intensity of the light emitting device 10L resultsin a white light.

FIG. 14A is a side sectional view of a first example of a light emittingdevice 10M fabricated on 6H:SiC (n-type) substrate 20M by doping withboron. The substrate 20M defines a first and a second side 21M and 22Mand a peripheral edge 2M. A first and a second Ohmic contact 61M and 62Mare electrically connected to the first and second side 21M and 22M ofthe substrate 20M.

Table 8 sets forth the parameters for the fabrication of the lightemitting device 10M of FIG. 11A. It should be appreciated by thoseskilled in the art that Table 8 is specific example and that numerousother parameters may be used to fabricate light emitting devices havingdifferent characteristics.

TABLE 8 Pulse Color repetition Focal Spot Scanning Contribution Powerrate Length size # of speed Dopant Sample in LEDs Dopant (W) (KHz) (mm)(μm) passes (mm/sec) medium 6H:SiC Blue-Green B 10.5 CW 150 100 1 0.8Boron Powder, n-type argon 30 psi Blue-Green B 12 5 150  80 2 0.8 Drivein, Argon 30 psi

FIG. 14B is a graph of light intensity as a function of wavelength forthe light emitting device 10M of FIG. 14A. The graph of FIG. 14Billustrates the distribution of light intensity as a function offrequency for the light emitting device 10M of FIG. 14A. The sum of thedistribution of light intensity of the light emitting device 10M resultsin a blue-green light.

Photovoltaic Device

FIG. 15 is a graph of is a graph of operational temperature as afunction of band gap for various solid sate devices. Silicon carbidedevices can operate at temperatures exceeding 650° C. [D. K. Sengupta,N. R. Quick and A. Kar, Journal of Laser Applications, pp. 21-26(2001).] which makes the material attractive as a thermoelectric device[P. M. Martin, “Thin film technology: thermoelectric Energy Conversion2: Thin film materials”, Vacuum Technology & Coating, pg. 8-13, (2007)and Y. Aoki et. al., “Study of Silicon Carbide Thermoelectric Materialsmade by SPS for MI-ID Power System”, 34th AIAA Plasma dynamics andLasers Conference, 23-26 June, Orlando, Fla., (2003)]. Wide bandgapsemiconductor p-n junction devices have potential for operatingtemperatures greater than 3000° C.

An optical device with p and n regions can produce electric current whenlight or electromagnetic radiation is irradiated on the device. Thesedevices are called photovoltaic cells. The photovoltaic device isfabricated using the same processing and p-n junction structure as ourwhite SiC light emitting diode (LED). The laser doping technology can beused to create any semiconductor structure including transistorstructures to create photovoltaic devices.

The p and n regions of the photovoltaic device were fabricated by laserdoping a n-type 6H—SiC (as-received nitrogen concentration of 5×10¹⁸cm⁻³) and p-type 4H—SiC (Al doped) (as received aluminum concentration1×10¹⁹ cm⁻³) wafer substrates with respective dopants. Cr and Al wereused as p-type dopants while N was used as n-type dopant. A Q-switchedNd:YAG pulse laser (1064 nm wavelength) was used to carry out the dopingexperiments. The experimental parameters for laser doping of Cr and Nwere: power 11-13 W, frequency 5-10 kHz for a spot size of 85-150 μm ata scan speed of 0.5-0.8 mm/s.

For n-type doping the sample was placed in a nitrogen atmosphere atpressure of 30 psi and laser-doped regions were formed on the samplesurface by moving the chamber with a stepper motor-controlledtranslation stage. The height of the chamber was controlled manuallythrough an intermediate stage to obtain different laser spot sizes onthe SiC substrate. For p-type doping, TMA (trimethylaluminum, (CH3)3Al)and Bis(ethyl benzene)-chromium were used. TMA was heated in a bubblersource immersed in a water bath maintained at 70° C. until it evaporatedand then a carrier gas, argon, was passed through the bubbler totransport the TMA vapor to the laser doping chamber. Similarly, forchromium doping Bis(ethyl benzene)-chromium was heated in a bubblersource immersed in a water bath maintained at 100° C. until itevaporated and then a carrier gas, argon, was passed through the bubblerto transport the ethyl benzene chromium vapor to the laser dopingchamber. These dopant gas species decompose at the laser-heatedsubstrate surface producing Al and Cr atoms, which subsequently diffuseinto the substrate.

Since crystalline SiC is chemically inert and has good thermo-mechanicalproperties at high temperatures, photovoltaic cells made of p-n regionsin SiC can be located at the walls of combustion chambers to directlyconvert radiative energy into electrical energy; particularly in powerplants. Burning fuels and the resultant flames produce electromagneticradiation in the ultraviolet (UV), visible and infrared regions of thespectrum. The combustion chamber is modified to contain stacks of SiCphotovoltaic cells so that each stack can absorb the radiation of aselected wavelength range to directly produce electricity.

Aluminum and Nickel were deposited on p and n regions respectively onthe samples prior to photocurrent measurements to serve as contacts.Contacts can also be laser synthesized producing stable carbon richconductors that can tolerate high temperatures beyond the capability ofconventional materials such as Al and Ni.

FIG. 16 is a side sectional view of a solid state photovoltaic device10N fabricated on 6H:SiC (n-type) substrate by doping with aluminum andchromium. The substrate 20N defines a first and a second side 21N and22N and a peripheral edge 23N. A first and a second Ohmic contact 61Nand 62N are electrically connected to the first and second side 21N and22N of the substrate 20N. The solid state photovoltaic device 10Nproduces an electric current between the first and second Ohmic contacts61N and 62N upon receiving electromagnetic radiation as indicated by theammeter 72 N.

Photocurrent measurements were conducted using a Keithleypico-ammeter/voltage source Model 6487 was used for carrying out thecurrent measurements, while an Agilent digital multimeter Model 34401Awas used for measuring the voltages and the resistances. The lightsource was a 50 W tungsten filament lamp.

With no visible light sources a background voltage and current existedin the SiC samples at room temperature (23° C.). Irradiation from a 50 Wtungsten filament light source produced a greater than 220% voltageboost and a greater than 4350% current output boost in the laser doped4H—SiC device. A greater than 540% voltage boost and a greater than1250% current output boost was observed in the laser doped 6H—SiCdevice.

The mechanism for the observed photocurrent SiC is as follows. When abroadband source of light impinges on the doped SiC structure, thephotons with different energies are absorbed, which creates electronhole pairs in the valence band. The photons with energies higher thanthe band gap of the substrate causes the electron to excite from thevalence band (or from impurity levels created by dopants Cr, Al, N) tothe conduction band (or same impurity levels). The electron flowsthrough the contact wires generate current and the correspondingvoltage.

The photovoltaic device can be laser doped with select dopants orcombination of dopants to absorb energy from the completeelectromagnetic spectrum. The photovoltaic device can be laser dopedwith select dopants or combination of dopants to select or filter therange of electromagnetic spectrum energy absorbed using the same laserdoping methods described for the LED wavelength emission selectivity.

The present disclosure includes that contained in the appended claims aswell as that of the foregoing description. Although this invention hasbeen described in its preferred form with a certain degree ofparticularity, it is understood that the present disclosure of thepreferred form has been made only by way of example and that numerouschanges in the details of construction and the combination andarrangement of parts may be resorted to without departing from thespirit and scope of the invention.

What is claimed is:
 1. The process of making a solid state energyconversion device for emitting green electromagnetic radiation uponexcitation by electrical energy, comprising the steps of: providing ann-type silicon carbide wide bandgap semiconductor material; applyingchromium dopant to a surface of the n-type silicon carbide wide bandgapsemiconductor material; directing a thermal energy beam onto the n-typesilicon carbide wide bandgap semiconductor material in the presence ofthe chromium dopant atoms for converting a region within the n-typesilicon carbide wide bandgap semiconductor material able to emit greenelectromagnetic radiation upon excitation by electrical energy; andforming Ohmic conductors for exciting the region of the n-type siliconcarbide wide bandgap semiconductor material with electrical energy. 2.The process of making a solid state energy conversion device foremitting blue electromagnetic radiation upon excitation by electricalenergy, comprising the steps of: providing an n-type silicon carbidewide bandgap semiconductor material; applying aluminum dopant to asurface of the n-type silicon carbide wide bandgap semiconductormaterial; directing a thermal energy beam onto the n-type siliconcarbide wide bandgap semiconductor material in the presence of thealuminum dopant atoms for converting a region within the n-type siliconcarbide wide bandgap semiconductor material able to emit blueelectromagnetic radiation upon excitation by electrical energy; andforming Ohmic conductors for exciting the region of the n-type siliconcarbide wide bandgap semiconductor material with electrical energy. 3.The process of making a solid state energy conversion device foremitting blue-green electromagnetic radiation upon excitation byelectrical energy, comprising the steps of: providing a n-type siliconcarbide wide bandgap semiconductor material; applying boron dopant to asurface of the n-type silicon carbide wide bandgap semiconductormaterial; directing a thermal energy beam onto the n-type siliconcarbide wide bandgap semiconductor material in the presence of the borondopant atoms for converting a region within the n-type silicon carbidewide bandgap semiconductor material able to emit blue-greenelectromagnetic radiation upon excitation by electrical energy; andforming Ohmic conductors for exciting the region of the silicon carbidewide bandgap semiconductor material with electrical energy.
 4. Theprocess of making a solid state energy conversion device for emittingred electromagnetic radiation upon excitation by electrical energy,comprising the steps of: providing a n-type silicon carbide wide bandgapsemiconductor material; applying chromium dopant to a surface of then-type silicon carbide wide bandgap semiconductor material; directing athermal energy beam onto the silicon carbide wide bandgap semiconductormaterial in the presence of the nitrogen dopant atoms for converting aregion within the n-type silicon carbide wide bandgap semiconductormaterial able to emit red electromagnetic radiation upon excitation byelectrical energy; and forming Ohmic conductors for exciting the regionof the silicon carbide wide bandgap semiconductor material withelectrical energy.
 5. The process of making a solid state energyconversion device for emitting orange-red electromagnetic radiation uponexcitation by electrical energy, comprising the steps of: providing ap-type silicon carbide wide bandgap semiconductor material; applyingchromium dopant to a surface of the p-type silicon carbide wide bandgapsemiconductor material; directing a thermal energy beam onto the siliconcarbide wide bandgap semiconductor material in the presence of thechromium dopant atoms for converting a region within the p-type siliconcarbide wide bandgap semiconductor material able to emit orange-redelectromagnetic radiation upon excitation by electrical energy; andforming Ohmic conductors for exciting the region of the silicon carbidewide bandgap semiconductor material with electrical energy.
 6. Theprocess of making a solid state energy conversion device for emittingwhite electromagnetic radiation upon excitation by electrical energy,comprising the steps of: providing a p-type silicon carbide wide bandgapsemiconductor material; applying chromium dopant and a nitrogen dopantto a surface of the p-type silicon carbide wide bandgap semiconductormaterial; directing a thermal energy beam onto the silicon carbide widebandgap semiconductor material in the presence of the chromium andnitrogen dopant atoms for converting a region within the p-type siliconcarbide wide bandgap semiconductor material able to emit whiteelectromagnetic radiation upon excitation by electrical energy; andforming Ohmic conductors for exciting the region of the silicon carbidewide bandgap semiconductor material with electrical energy.
 7. Theprocess of making a solid state energy conversion device for emittingwhite electromagnetic radiation upon excitation by electrical energy,comprising the steps of: providing an n-type silicon carbide widebandgap semiconductor material; applying chromium dopant and aluminumdopant to a surface of the n-type silicon carbide wide bandgapsemiconductor material; directing a thermal energy beam onto the siliconcarbide wide bandgap semiconductor material in the presence of thechromium and aluminum dopant atoms for converting a region within then-type silicon carbide wide bandgap semiconductor material able to emitwhite electromagnetic radiation upon excitation by electrical energy;and forming Ohmic conductors for exciting the region of the siliconcarbide wide bandgap semiconductor material with electrical energy.